1. Field of the Invention
The present invention generally relates to an on-vehicle electronic device, such as a car stereo device, and more particularly to an on-vehicle electronic device having burglarproof function.
2. Description of the Related Art
There are two types of car stereo devices. A first type of the car stereo devices is fixedly or permanently installed in a cockpit, and a second type thereof is detachably installed. The car stereo devices of the second type can be protected against burglary by detaching them from the cars when the users leave the cars.
There are, as detachment mechanisms for such car stereo devices of detachably installed type, a partially detachable system and a totally detachable system. In the partially detachable system, only essential parts of the car stereo device are detached from the cockpit. In the totally detachable system, the whole car stereo device is detached from the cockpit.
A description will now be given for the partially detachable system.
In the partially detachable system, an operation panel is detachably mounted in front of a cabinet which is fixed to the vehicle. A cassette tape is inserted into the cabinet via an opening. Main parts of the car stereo device are provided in the operation panel. Hence, the car stereo device with the operation panel detached therefrom does not function. In this manner, the above detachment mechanism of the operation panel substantially serves as a burglarproof means.
A mechanical switch for detecting the presence of the operation panel is attached to the cabinet. When the operation panel is mounted into the cabinet, a projection provided on a back surface of the operation panel comes into contact with the mechanical switch, and presses it. Thereby, the mechanical switch is turned ON. Then, the turned ON signal of the mechanical switch is detected as a signal indicating whether or not the operation panel is mounted to the cabinet.
However, the above-mentioned car stereo device of the partially detachable type has the following disadvantages. First of all, in order to detect the presence of the operation panel, it is necessary to provide the mechanical switch and a circuit for detecting the state of the switch. This needs a complex configuration and increases the production cost.
Secondly, in this car stereo device, even if an operation panel of another electronic device is mistakenly mounted into the cabinet, the detection mechanism detects the presence of the operation panel since the mechanical switch is operated even by the mistakenly mounted electronic device. In other words, the detection mechanism of this type of car stereo device cannot detect the fact that another operation panel is mistakenly mounted.
In another detection mechanism for such car stereo devices of detachably installed type, there are provided terminals fastened to the cabinet, such that one terminal is connected to the mechanical switch, and the other terminal is grounded. Further, there are provided terminals, which are short-circuited, fastened to the operation panel at positions facing to the terminals of the cabinet.
Accordingly, when the operation panel is placed in position, a current path is established between the cabinet and the operation panel via the terminals only when an appropriate operation panel is mounted. Thus, if the operation panel of another electronic device, which has terminals located at positions different from those of the terminals of the pertinent operation panel, is mistakenly mounted to the cabinet, no current flows through the terminals, so that the judgement whether or not an appropriate operation panel is mounted can be performed by use of the current flow through the terminal.
However, this type of detection mechanism using the terminals, essentially has a following problem. Namely, it is necessary for the operation panels of electronic devices of different types to have the terminals located at different positions, resulting in the increases of the cost and difficulty of the production.
It will be noted that other detachable audio devices, such as radios, have disadvantages as described above.